Since 1980, I believe this has become even worse, more like 80-20 or 90-10.

Why is that?

This only makes logical sense when interpreted as a side-effect of our
plurality
voting system – "who the leading two horses are"
is key strategic knowledge for any voter in that system (since without that knowledge, voters
would be incapable of voting strategically and would be at great risk of "wasting" their vote
by, e.g, foolishly voting for their true favorite).
Crazily, "horse race"
information therefore actually is among the most important information
a voter can have under the present plurality voting system, and information about the actual
views of any candidates besides the top two is usually of near-zero true importance.

If we were using a better voting system such as
range
or
approval
voting, then voting your favorite top is never strategically unwise, so
the candidates' actual views become much more important,
and strategy comparatively less important.